This application claims the priority of German patent document no. 10 2006 046 001.4, filed Sep. 27, 2006, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for adjusting the integrity alert threshold in a satellite navigation system.
In the future European Galileo satellite navigation system, an integrity data stream will be available which permits the signaling of system or satellite failures to users. In particular, faulty satellite signals can be provided with integrity warnings.
The Galileo, it should be noted, will differentiate among different user levels as follows: Users of level A are dynamic applications with a high horizontal and vertical position precision, such as airplane approaches, or the locating of trains on secondary lines. In contrast, users of level B have lower demands on the position precision, such as aviation en-route. Finally, the position precision demands are the lowest for users of level C. Such users are, for example, maritime applications.
The Galileo integrity concept provides that the processing facility of the ground segment of Galileo makes a prediction concerning the precision of navigation signals. This prediction is called an expected signal error or signal in space accuracy (SISA). The actual errors of the individual navigation signals emitted by satellites or signal in space errors (SISE) are estimated by observations of the monitoring network of the Galileo system. The estimated errors are called estimated SISE (eSISE). According to the integrity concept, it is a satellite is set to “not serviceable” by way of an alert (IF: integrity flag) as soon as the estimated signal error eSISE of this satellite is greater than an integrity alert threshold (TH: threshold).
Since the integrity alert thresholds differ for the above-mentioned user levels, (particularly the threshold for users of level A, which is the lowest), this has the result that satellites which are not serviceable for a level A user are also not serviceable for a level B and C user. Significantly, if separate alerts existed for the level B and C users, they would still be serviceable; however, the transmission rates for alerts do not permit separate alerts for the different user levels.
In the Galileo system, the integrity alert threshold is calculated as the product of a pre-factor and the root of the sum of squares of the expected signal error (SISA) and of the precision of the signal observation or signal in space monitoring accuracy (SISMA), as follows:TH=kpfa·√{square root over (SISA2+SISMA2)}
The pre-factor kpfa is determined by the permitted false alert rate.
One object of the present invention is to provide a method of adjusting the integrity alert threshold in a satellite navigation system, such that different integrity demands, particularly for different user levels, can be satisfied by means of a data stream.
This and other objects and advantages are achieved by the method according to the invention, which includes changing one or more parameters in a data stream emitted by a satellite of a navigation system, which parameters cause an adjustment of the integrity alert threshold. In addition, the invention also provides for differently interpreting a data stream emitted by a satellite of a navigation system, particularly in a receiver, specifically in such a manner that the satellite navigation system is classified as serviceable under conditions which differ from previous conditions.
Another feature of the invention provides a computer program for implementing a method according to the invention if the computer program is carried out on a computer. The computer program may be stored on a data carrier, for example, a visual data carrier such as a CD-ROM or DVD, a magnetic data carrier, such as a floppy disk, or an electronic data carrier, such as a memory card.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.